The induction of metal binding protein e.g. metallothionein, with the subsequent localization of metals in subcellular components e.g. chromatin, following exposure to sublethal levels of cadmium copper and mercury is studied in mice. Highly purified metal binding proteins and chromatin fractions are isolated after varying periods of exposure to overdoses of the respective metals (usually 10 to the minus 3rd power M Hg or Cd or 10 to the minus 2nd power M Cu) and are characterized by metal content, spectrophotometry, thermal stability, electrophoresis, viscosity and other parameters. The mechanism of induction will be explored by fractionation and further analyses of chromosomal material into the substituent components of euchromatin and heterochromatin. The study should give insight into cellular events which enable an animal to tolerate levels of metals usually considered toxic and should contribute to our understanding of the regulation of specific gene expression.